1. Field of the Invention
This invention relates to a supersonic wave device for a vehicle with which a vehicle height in respect to a road surface and the like is detected by use of a reflected wave of a supersonic wave sensor installed in the vehicle. More particularly, this invention relates to an apparatus for preventing a roundabout of a supersonic wave in which the supersonic wave transmitted from a transmitter in the supersonic wave transmitter and receiver of the vehicle is directly received by the receiver without being reflected by the object.
2. Description of the Prior Art
Hitherto, there are developed various supersonic wave sensors in which a distance to an object and the presence or non-presence of the object are detected by the reflected wave of the supersonic wave sensor. In the vehicle itself, various supersonic wave sensors have been developed as the performance of the vehicle has been improved. In particular, there is a supersonic wave sensor for a road surface to be used in a so-called supersonic wave suspension, such as a vehicle retracting sensor, for sensing the obstacles at the rear part of the vehicle or a so-called backsoner, for example, in which a variation in vehicle height is measured in response to a condition of the road surface such as a bad road during running of the vehicle. A dampening force of the shock absorber is properly controlled to improve a comfortable feeling and stability in steering.
FIG. 8 shows a side elevational view for illustrating the conventional type of the supersonic wave sensor.
As shown in FIG. 8, a sender is provided for transmitting a supersonic wave to a receiver 2 for receiving a supersonic wave sent from the sender 1.
An insulator 3 protects the sender 1 and the receiver 2 and is made of foamed rubber and the like.
A base plate 4 is provided for mounting circuit elements 5 which are protected by a filler agent 6. A reference numeral 7 denotes a case.
In the case 7 is formed an inverted cone shaped horn 8 at the front surface of the sender 1 and the receiver 2. In the surface to which the horn part 8 is opened is held a heater 9 by a bracket 10.
In this type of conventional system having the above-described components, the supersonic wave transmitted from the sender 1 reaches the receive 2 through a diffraction and a side lobe and the like as a direct wave in the air. As another passage for the supersonic wave, it is transmitted through a clearance formed between the case 7 and the heater 9 and an assembly of the bracket 10.
A phenomenon in which the supersonic wave is transmitted directly from the sender 1 to the receiver 2 is defined as a so-called roundabout phenomenon of the supersonic wave. In order to prevent an erroneous operation of the system caused by this roundabout phenomenon, for example, as shown in FIGS. 6 and 7, it was necessary to provide a procedure for electrically inhibiting a sensing of the received signal caused by the roundabout of the supersonic wave under an operation of the circuit during a desired time T1 (m sec) from a time t.sub.0 (m sec) of transmitting the supersonic wave. A characteristic (i) shown in FIG. 6 indicates a charcteristic of the received signal caused by the roundabout of the supersonic wave, and a characteristic (j) indicates a characteristic of the received signal caused by a reflected wave from the sensed objects of the supersonic wave sensor, for example, the road surface and the like. FIG. 7 shows a characteristic of a timing pulse for use in energizing the sender 1. Therefore, if the continuing time of the roundabout characteristic (i) of the supersonic wave is extended, it is necessary to set a long prohibiting time T1 (m sec). In other words, the object placed at a short distance where a reaching time of the reflected wave to the receiver 2 is short cannot be sensed. This feature is a fatal disadvantage in the supersonic wave road surface sensor for use in sensing the road surface placed at a short distance from the vehicle.
That is, in the supersonic wave sensor for use in sensing a short distance object such as a supersonic wave road surface sensor, it has been the final subject to shorten the duration time of a roundabout phenomenon of the supersonic wave or to reduce the roundabout phenomenon of the supersonic wave.